Many vehicles are equipped with steel or glass access doors that are pivotably attached to the vehicle about the upper edge of the door. Such access doors, referred to herein as "rear lift gates", can be opened by raising the lift gate, thereby exposing the passenger compartment. Frequently, torque-assist pneumatic cylinders are connected between a rear lift gate and vehicle body to assist in raising the lift gate, when a person lifts upwardly on the lift gate.
It happens that in many vehicles, rear lift gates (and other doors on the vehicle) cannot properly be opened unless a person first transmits a security signal from a hand-held transmitter to the vehicle. In other words, many vehicles are equipped with electronic security systems which incorporate user-generated authenticating signals to disarm the security system and thereby permit access to the interior of the vehicles.
For example, the Viper.RTM. coupe made by Dodge has only a single lock cylinder, with the lock cylinder being associated with a rear lift gate window, and the doors of the vehicle can be opened only after transmission of the security signal. While effective, it happens that such security systems can be bypassed by, e.g., breaking the rear lift gate window or by opening the lock cylinder with a master key.
Not surprisingly, systems have been provided which incorporate switches for generating electrical signals when a rear lift gate is open. For example, U.S. Pat. No. 5,003,136 to Valenzona discloses a switch that can be engaged with a rear lift gate assist cylinder to generate a signal when the lift gate is open. Unfortunately, the device disclosed in Valenzona is comparatively complicated, in that it incorporates first and second telescoping sleeves that are spring-loaded in an outer housing, with each sleeve being associated with a respective electrical contact. The sleeves reciprocate relative to each other within the outer housing when the lift gate moves, thereby causing the contacts to touch and generate an electrical signal. Thus, the Valenzona device requires a relatively large number of components and springs which must move relative to each other, in addition to the movement of the torque assist strut within the cylinder. As recognized herein, however, it is possible to provide a simple, inexpensive switch for generating an alarm to indicate unauthorized entry through an access door having a torque-assist cylinder.
Accordingly, it is an object of the present invention to provide a method and apparatus for generating an alarm signal to indicate the unauthorized opening of a vehicle access door. Another object of the present invention is to provide a method and apparatus for generating an alarm signal that uses existing torque assist cylinders. Yet another object of the present invention is to provide a method and apparatus for generating an alarm signal when a rear lift gate door is opened without electronic authorization. Still another object of the present invention is to provide a method and apparatus for generating an alarm signal in a vehicle which is easy to use and cost-effective.